1、INTERNATIONAL TELECOMMUNICATION UNION ITUWT TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU M.1230 (05/9 6) SERIES M: MAINTENANCE: INTERNATIONAL TRANSMISSION SYSTEMS, TELEPHONE CIRCUITS, TELEGRAPHY, FACSIMILE AND LEASED CIRCUITS International public telephone network Method to improve the management
2、 of operations and maintenance processes in the International Telephone Network ITU-T Recommendation M.1230 (Previously wCCITT Recommendation) ITU-T M-SERES RECOMMENDATIONS MAINTENANCE: INTERNATIONAL, TRANSMISSION SYSTEMS, TELEPHONE CIRCUITS, TELEGRAPHY, FACSIMILE AND LEASED CIRCUITS Introduction an
3、d general principles of maintenance and maintenance organization International transmission systems M.300-M.559 International telephone circuits M.560-M.759 M.760-M.799 M. 800-M. 899 M.900-M.999 M. 1000-M. 1099 M.llOO-M.1199 M. 10-M.299 Common channel signalling systems International telegraph syste
4、ms and phototelegraph transmission International leased group and supergroup links International leased circuits Mobile telecommunication systems and services International data transmission systems M.1300-M.1399 Designations and information exchange M.1400-M.1999 International transport network M.2
5、000-M.2999 Telecommunications management network M.3000-M.3599 Integrated services digital networks M.3600-M.3999 Common channel signailing systems M.4000-M.4999 For further details, please refer to ITU-T List of Recommendations. FOREWORD The ITU-T (Telecommunication Standardization Sector) is a per
6、manent organ of the International Telecommunication Union (). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Confer
7、ence (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the IT-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, Mar
8、ch 1-12, 1993). IT-T Recommendation M.1230 was revised by ITU-T Study Group 4 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 12th of May 1996. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication admi
9、nistration and a recognized operating agency. O ITU 1996 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation M.1230 (0519
10、6) I . STD-ITU-T RECMN M.1230-ENGL 177b Li8b2571 Ob21817 4b4 CONTENTS 1 scope 2 General . 3 Assessment of network performancefrom the point of view of maintenance . 4 Major NF parameters for end-to-end measurements 5 Review of present methods for assessing overall (end-to-end) network performance .
11、Service Quality observations (non-intrusive measurements) 5.1 Test calls methods (intrusive measurements) . 5.2 5.3 Considerations of the methods of network performance assessment 6 General method for the optimization of the Operations and Maintenance (OBrM) processes . Annex A - Example of Context
12、Difficulty Index (CDI) in an O revised in 1996) 1 Scope This Recommendation provides a reference model which includes both the description of the main parameters and different methods to assess the network performance. The description of a Context Difficulty Index (CDI) which is related to several c
13、omponents of the network and the O ii) standardize any specific O iii) establish any specific objectives, target and thresholds for QOS and NP parameters; iv) set any level of Customer Satisfaction. The choice or decision on ail the above issues is left to individual TO or to specific arrangements b
14、etween TOS (e.g. when TOS jointly establish formal Service Quality Agreements with the major aim to develop mutually acceptable performance standards and to enable customer expectations to be met 141). 2 General With the increased liberalization and consequent competitive telecommunication scenarios
15、, there is an increased need to find out in various ways how the network is performing to meet customer expectation. All Network and/or Service Providers, who in the past provided only network capacity and then maintained performance level by using different maintenance methods specified in ITWT Rec
16、ommendations, are now more and more focused on the improvement of Np and QOS) as experienced by customers. To meet these main objectives, each TO has introduced and developed a wide range of test procedures and quality assessment methods2) in order to test the network both objectively and subjective
17、ly and to ensure a better and better QOS to their customers i to 201. It is also very important to note that modem telecommunication systems have a great deal of built-in facilities through which it is possible to ensure a continuous and automatic supervision of performance parameters. ) QOS is defi
18、ned as “the collective effect of service performance which determines the degree of satisfaction of a user of the service” 161. Thus QOS is of concern to the user of the Service Provider. When the Network Provider is also the Service Provider he is responsible for the QOS. 2, Continuous interrelatio
19、nship and exchange of information in this area is necessary between ITU-T SG 4 and SG 2. in fact many Recommendations of E-Series describe QOS and NP concepts, parameters and methods for their measurements and they also contain suggestions on how to establish Service Quality Agreements i141 and also
20、 Customer Satisfaction Point 131 between Telecommunications Operators. Recommendation M.1230 (05196) 1 3 Assessment of network performance from the point of view of maintenance National network *Network Performance (NP)* is a statement of the performance of connection element or concatenation of con
21、nection elements employed to provide a service and it is defined and measured in terms of parameters which are meaningful to Network Providers for different purposes 16. Furthermore, it is to be noted that NP is defined independently of terminai performance and customer?s actions and it is also serv
22、ice independent in that it must be able to support all the services the particular network is required to transport. International National network network The QOS experienced by a customer is a very broad concept and depends on a combination of factors some of which are not under the direct respons
23、ibility of maintenance staff, for example: - calling and called customer behaviour (Le. percentage of non-successful calls related to premature abandonment or not answered calls for various reasons such as ring tone no answer, busy tone received or subscriber busy, etc.); - planning and provisioning
24、 of the network and whether sufficient network resources (i.e. circuits, switching equipment) are provided to meet the number of call attempts by customers (e.g. percentage of non-successful calls due to lack of tninks/circuits); - the degree to which network management or any other control system o
25、r tool is employed. It should be emphasized that the assessment of network performance is of primary importance to Network Providers for the ?efficient maintenance? of their international telephone network 191. Therefore, it is very important to assess the network performance through end-to-end meas
26、urements and to collect all results in order to activate any corrective maintenance action as needed to re-establish the level of performance as required. From the point of view of Maintenance, the assessment of international telephone network performance involves a measurement of the capability of
27、the overall network (end-to-end, i.e. international section plus two national sections), to establish a switched connection of good transmission quality whenever required. The general reference model for overall (end-to-end) measurements is reported in Figure 1. Network I _I End-teend path Customer
28、I I I I Customer CTE I I I I LE+TE ISC IN ISC TE+E CTE LE LocalExchanga TE Transit Exchange ISC International Switching Centre IN International Network Customer?s Terminal Equipment (e.g. telephone, data terminal, fax terminal, etc.) FIGURE 1M.1230 Reference model for overall (end-bend) measurements
29、 2 Recommendation M.1230 (05196) 4 Major NP parameters for end-to-end measurements According to existing Recommendations, the parameters essential to objectively measure the Quality of Service as perceived by customers, may be categorized into two main areas 12: a) Call connectiviq The essential par
30、ameters required to assess the connectivity quality are: 0 0 Start Dial Signal Delay (SDSD); Call disposition (e.g. reasons for unsuccessful call completion, e.g. wrong number, unknown tone, congestion, etc.); 0 Post Dialling Delay (PDD); 0 Call failures are categorized as due to network faults, equ
31、ipment failure and network congestion. Call Completion Rate or Answer Seizure Ratio (ASR). b) Transmission quality The essential parameters contributing to the transmission quality (call clarity) are: Transmission loss; 0 Attenuation distortion; Total distortion; 0 Group delay distortion; 0 Idle cha
32、nnel noise; Impulsive noise; 0 Round-trip delay; Echo; o Clipping. It is important to note that for compatibility between manufacturers and TOS, it is essential to have a common measurement methodology3). This will ensure that measured results are comparable between TOS and thus it will improve thei
33、r cooperation in all joint activities and also the quality of the telephone service as offered to mutual customers. As examples of network parameters, a list of main parameters for voice and non-voice calls is given below. This is not an exhaustive list. Voice - Circuit loss; - Circuit noise; - Impu
34、lsive-noise; - Cross-talk (unintelligible); - Terminal balance; - - Propagation time, digital processing; - Impedance mismatch; - - - Echo, control devices, delay, loss, stability; Quantization, non-linear and attenuation distortions and bandwidth; Speech detectors parameters, switched loss clipping
35、, interruptions, freeze-out, fading; Power loads on cables and carriers, leakage, imbalances. 3, This requires further studyldefinition. 3 Recommendation M.1230 (05196) Non-voice - - Burst errors; impulsive-noise, frame slips, jitter, hits, drop-outs, distortion, circuit loss, cross-talk, interrupti
36、ons; - Echo; - Delay; - Out of synchronism; - Noise; - Group delay distortion. 5 Review of present methods for assessing overall (end-to-end) network performance At present the following methods of measuring international telephone networks are available. 5.1 Test calls methods (intrusive measuremen
37、ts) There are currently four types of test calls which can be carried out both manually or automatically to assess the functioning of international circuits, namely 4: a) Type I test calls These test calls are conducted between two directly connected international centres to verify that the transmis
38、sion and signalling performance on an intemational circuit of a given group are satisfactory. b) Type 2 test calls These test calls are conducted between two international centres not directly connected to verify transit operational facilities of an intermediate international centre. c) Type 3 test
39、calls These test calls are conducted from an international centre to a subscriber type number in the national network of the distant country (in general as a result of a particular kind of fault). d) Subscriber-to-subscriber type test calls These type of test calls are conducted with test equipment
40、having the characteristics of an average subscriber line in one national network to similar equipment in the national network of a distant country. The main existing Recommendations that describe subscriber-to-subscriber end-to-end measurements are: - Recommendation M.1235 - “Use of automatically ge
41、nerated test calls for assessment of network performance” 20 This Recommendation describes the use of automatic subscriber-to-subscriber test calls performed either in system-independent test call generators and test call responders, or by built-in facilities performing the same functions. Call-thro
42、ugh testing as described in this Recommendation, can be used to check the performance on routes, circuits, switches and associated equipment. It should be noted that these test calls programmes should be carried out both during non-busy and busy periods and they have to be carefully planned. This me
43、ans they have to be agreed between TOS concerned in order to avoid any kind of interference by a contemporaneous use of the same test number for other utilization. In this Recommendation are also defined the criteria for the choice of the number of test calls to be generated towards each switched de
44、stination and as it is stated, this number is mainly dependent on the frequency of difficulties encountered towards a certain destination (i.e. fewer test calls are needed to identify the network performance level when the rate of difficulties encountered is high). 4 Recommendation M.1230 (0996) - R
45、ecommendation E.434 - “Subscriber-to-subscriber measurements of the public switched telephone network77 121 This Recommendation defines the methods and processes for testing, the measurements required, the elements of an end-to-end system and the operation of an end-to-end system, and it also contai
46、ns Recommendations to define interfaces and protocols. It is to be noted that also in this Recommendation the number of test calls depends on the parameters to be measured and the desired accuracy for those parameters. Further the number of test calls should be large enough to provide statistically
47、valid results within the desired accuracy for each parameter measured, and small enough to allow the data to be collected over a fairly short period of time. Particular consideration should be given to trunk size of traffic volumes on the route when test call quantities are being determined. Another
48、 consideration (limitation), is to keep the best period for measurements relatively short to ensure the availability of the test device, and therefore to avoid conflicts that might result in the use of responders. It is important to observe that “such conflicts” could also have an impact on the accu
49、racy of results as test calls may have failed to complete because the terminating responder was in use for a different test programme rather than a real network failure. In conclusion, also this method requires careful coordination and scheduling for test calls programmes between the TOS concerned. 5.2 Service Quality observations (non-intrusive measurements) Another way of supervising the total through connection capabilities of the network is to make Service Quality observations. The definition of “Service observation” 2 is the following: “Monitori
